1. Field of the Invention
This invention pertains generally to devices and methods for finishing the surfaces of wood and fiberboard items, and more particularly to an apparatus and method for applying decorative coating from a foil onto curvilinear and irregular-shaped edges of wood pieces without the need for a template or other guide structure.
2. Description of the Background Art
As dimensional lumber is becoming increasingly scarce and expensive, much furniture is now made from board material comprising pressed and bonded sawdust, wood chips or wood fibers, such as reconstituted fiberboard, chip board and medium density fiberboards or MDF. In its natural state, MDF and other fiberboard materials are somewhat unattractive and do not provide finished surfaces suitable for use as furniture or for decorative applications. In order to make MDF and other fiberboard look more like the dimensional lumber it replaces, it is desirable to cover the board surfaces with a decorative film which simulates a wood grain finish. This is carried out by various surface finishing treatments to improve the physical appearance of the MDF. A frequently used surface finishing treatment process is foiling, wherein a wood grain pattern or other decorative pattern is painted onto a roll of plastic carrier film or tape, and then, using heat and pressure, the decorative paint pattern is transferred from the film to the MDF surface. The foil typically comprises a carrier film such as MYLAR.RTM. polyester, a heat release adhesive adjacent to or on the carrier film, a layer of decorative paint or pigment placed on the heat release adhesive, and a heat activated adhesive on top of the decorative paint layer. When the foil is heated and pressed against a substrate such as the edge of a board, the heat activated adhesive sticks to the substrate while the heat release adhesive is released or disengages from the carrier film, thus providing for transfer of the decorative paint layer to the board from the film.
In the past, edge foiling of rectangular boards has been carried out in four separate passes by various types of machines. More recently, single pass edge foiling of all four edges of rectangular boards, as well as contoured edges of non-rectangular boards, has been achieved through use of a template which exactly matches the shape of the edges of the board which is to be foiled. The template generally has a guide structure associated with its edges, such as a chain which can be driven by a sprocket. The template pattern serves to hold the board against the foiling wheel from which the decorative foil is transferred to the board edge.
Several drawbacks are associated with conventional edge foiling devices and other surface finishing devices and methods which require templates. For example, surface finishing machines generally require that each board have its own template with a precise edge pattern that matches the board. The template patterns are costly to build, maintain and store, and use of template edge foiling devices requires that the board have exactly the same shape as the template pattern, or the foil will not be applied properly to the board edges. In order to carry out edge foiling of a different-shaped board on the foiling device, there is necessary delay because the previous template must removed from the device and a new template installed thereon which matches the edge contours of the new, different-shaped board to be finished.
Another important problem present in conventional edge foiling machines is that the boards are moved with a constant speed in relation to the chain on the template, rather than at the appropriate or optimum speed for the particular edge or peripheral contour of the board which is being foiled. This results in a peripheral speed which varies with the shape of the board edges and causes uneven application of the decorative coating from the foil onto the board edges. A certain amount of heat and pressure for a given amount of time is required for proper foiling. Conventional edge foiling machines which vary the peripheral speed of the board tend to apply heat and pressure from the foiling wheel onto the board for too much time in the straight sections of edges, and for too little time in the corners and curved sections of the edges, thus resulting in uneven application and poor adhesion of the foil to board edges.
Yet another deficiency in conventional edge surface finishing devices is that scratching or marring of previously top-finished and/or bottom finished board surfaces may occur during edge finishing due to the manner in which the machines hold the boards during the edge finishing operation.
Accordingly, there is a need for a surface finishing apparatus for MDF boards and the like which does not require the use of templates or guide structures, which can be used for edge-foiling or edge finishing of boards having irregular and curvilinear edge structures, which can consecutively carry out edge-finishing on different shaped boards without requiring exchange of templates or other machine adjustment between boards, and which does not damage previously finished top and bottom surfaces. The present invention satisfies these needs, as well as others, and generally overcomes the deficiencies found in conventional foiling machines.